This invention relates to an apparatus for ultrasonic diagnosis and more particularly to the structure of its part for setting the number of focusing steps.
Most apparatus for ultrasonic diagnosis are capable of a so-called B-mode display, forming and displaying tomographic images on the basis of ultrasonic echoes. Such an apparatus is normally capable of changing the image size in several steps, allowing its operator to change the image size according to the depth of the target body part of a patient which is being diagnosed. Ultrasonic beams can thus be focused at the target positions of diagnosis, and the operator can obtain a tomographic image showing such target positions clearly.
Some of such apparatus for ultrasonic diagnosis adapted to make B-mode displays are also capable of increasing the number of focusing steps in the direction of the depth such that an image with improved azimuthal resolution at all levels of depth can be obtained by focusing the ultrasonic beams at every selectable level of the target body part. It is not the case, however, that a clear image can always be displayed under all circumstances by using such an apparatus and by switching the depth for disgnosis and the number of focusing steps.
If the depth of the target position is increased and the frame rate becomes less than the frame rate of a video output, for example 30 in NTSC system, such that the transmission and reception of ultrasonic waves and the formation of an image cannot be carried out at the timing for the display, the display of formed images may take place at a delayed timing, or some images may be skipped. In other words, a correct display may not be obtained in such a situation, and what the operator observes may not be what is actually taking place at the time of the observation.
If the number of focusing steps is increased, the azimuthal resolution improves all over the display screen and it becomes possible to obtain an image with improved overall clarity. On the other hand, however, since the frequency of wave transmission and reception in each direction increases, the frame rate decreases accordingly in such a case and it becomes impossible, as explained above, to capture the real-time movements of the target body part.
In view of the above, the prior art procedure has been to set the image size and the number of focusing steps appropriately, to observe the displayed image under these set conditions and then to adjust the image size and/or the number of focusing steps, depending on the condition of the observed displayed image. This means that the operator had to go through a series of cumbersome time-consuming operations before a reasonably clear and sufficiently accurate real-time image could be displayed. If the operator was not sufficiently skilled, furthermore, a satisfactorily accurate image could not be displayed at times.